With reference to FIG. 1, the relation of the voltage with respect to time of the actuation of an HID lamp is illustrated. In FIG. 2, the relation of the current with respect to time of the actuation of the HID lamp is illustrated. When the HID lamp is actuated, the internal gas will convert to a form of plasma. The voltage between two electrodes of the lamp tube will operate with a specific range. When the HID lamp is steady, the light efficiency of the HID lamp is controlled by adjusting the current, while the variation of the voltage between the two electrodes is small.
The power sources of the HID lamps may be AC source or DC source. After an HID lamp is light up, to sustain the temperature between the two electrodes, if the temperature of the electrodes descends too quickly, the electrons cannot be stimulated. Then the HID lamp will distinguish.
To control the HID lamp lights efficiency is to adjust the input current of the HID lamp. Generally, an HID lamp is an intrinsic light efficiency. The control process is that to actuate the HID lamp with a normal light efficiency. After the HID lamp is steady, the input current is adjusted to control the light efficiency of the HID lamp.
However, this control way needs to change the structure of the ballast of the HID lamp, while this is inconvenient.